Conventionally, an image forming device, such as a printer, a copier, a facsimile machine and a multifunction machine, for example a color printer, has image forming units of colors of black, yellow, magenta and cyan. A photoreceptor drum is charged by a charge roller at each of the image forming units, a latent image is formed by a light emitting diode (LED) head exposing the photoreceptor drum, and a toner image of each color is formed by electrostatically adhering toner that is a developer on a developing roller. The toner is formed in a thin-layered manner on the developing roller for the latent image.
Then, each toner image is transferred onto a carried sheet in order by a transferring roller in accordance with a transferring belt running along with each image forming unit, and each of the color toner images are formed. Subsequently, the sheet is sent to a fuser, the color toner images are fused on the sheet at the fuser. The color image is formed.
With this kind of printer, it is necessary to detect the density of the toner image of each color in order to adjust the color image. In order to do so, the predetermined shaped image is formed as a density detecting pattern on the transferring belt by the toner of each color. Subsequently, the density of image part of each color that structures the density detecting pattern is detected, and the voltage that is applied to the developing roller, in other words, the developing voltage is corrected based on the detected density. Accordingly, density of each toner image can be corrected and the color image can be adjusted. (for example, see Japanese laid-open patent application number 2004-341100)
However, with the conventional printer, for example, when the toner is overly charged due to the temperature and moisture around the printer or the like, the density of the toner image of each color becomes high beyond the density range. As a result, the density of each toner image cannot be corrected by only correcting the developing voltage. The color image cannot be adjusted sufficiently; therefore, the image quality decreases.
The present application shows an image forming device that can solve the problems of the conventional printers, and can improve image quality even when the developer is overly charged due to the environmental changes.